The present invention relates to a shaped body of carbon, in particular a carbon electrode, preferably having a largely round cross-section and being provided in its surface with at least one slot extending in a generally longitudinal direction and extending to the inside of the body.
Carbon electrodes have been utilized for many years in electro-thermal processes. There is widespread use of graphite electrodes in electric steel furnaces of graphitized as well as non-graphitized carbon electrodes for the manufacture of ferro alloys, calcium carbide, phosphorus, etc. The carbon electrodes in these processes serve to conduct electricity in which connection they are exposed to very high temperatures. For example, the tip of the graphite electrode in the steel furnace attains an average temperature of about 2000.degree. to 2200.degree. C. and for a short period a temperature above 3500.degree. C. at the base of the electric arc.
Although carbon electrodes generally withstand these high temperatures due to the high sublimation point of carbon, which is at approximately 3500.degree. C., disadvantageous effects can result primarily when the electrodes are subjected to very high alternating temperature stresses, so-called thermo-shocks. Such a thermo-shock occurs for example when the electrodes after tapping of an electric steel furnace, are withdrawn from the hot furnace and are exposed to the cold ambient air. The result in that case is a certain, extensive cooling and shrinking of the outer zone, and, thus, a high peripheral tensile stress. This very often then entails crack formations. Generally, such cracks develop irregularly, but there is an accumulation of them in the nipple regions, i.e. at the ends of the electrode where the cross-section is relatively weaker. Because of the usually higher coefficient of transverse thermal expansion of the nipple, the mechanical load of the electrode material becomes very high in these regions, apart from the weakening in cross-section, and may exceed the strength of the material. The cracks caused by thermo-shocks advesely affect the melting process because pieces of the electrode frequently break off, drop into the melt, and thus cause carburization of the melt. Further, cracked electrodes also are subject to greater burn-off, resulting in a great increase in electrode consumption per ton of steel.